BACKGROUND OF THE INVENTION:
Field of The Invention
[0001] The present invention relates to apparatus and method for optimally controlling a
damping force characteristic of a suspension system of an automotive vehicle, the
suspension system having four shock absorbers, each shock absorber being interposed
between an sprung mass of the vehicle body and an unsprung mass of a corresponding
one of front left and right and rear left and right road wheels.
Description of Background Art
[0002] A Japanese Patent Application First Publication No. Hesei 4-191109 exemplifies a
previously proposed suspension system for controlling a damping force of each shock
absorber interposed between a sprung mass of a vehicle body and an unsprung mass of
a corresponding one of front left and right road wheels and rear left and right road
wheels.
[0003] The previously proposed suspension system includes: an actuator which is so arranged
and constructed between the vehicle body and rear road wheels as to enable to increase
and decrease a supporting force of a vehicle body on the rear road wheel; vibration
input detecting means for detecting a vibration input from each of the front road
wheels due to a passage of the vehicle on a road surface convex and recess; vehicle
speed detecting means for detecting a vehicle speed; and controlling means for controlling
an operation of the actuator on the basis of the inputs from the respective detecting
means.
[0004] The controlling means calculates a time point at which the rear road wheels will
pass on the same road surface convex and recess which has given the vibration inputs
exceeding a predetermined value on the basis of the output vehicle speed of the vehicle
speed detecting means when determining that the vibration inputs from the front road
wheels have exceeded the predetermined value and is so arranged and constructed as
to operate the actuator so that, at that time point, the vibration inputs from the
rear road wheels are relieved. That is to say, the previously proposed suspension
system carries out a, so-called, preview control such that a timing at which the vibration
inputs from the front road wheels are used as correction signals on the respective
rear road wheel positioned shock absorbers is delayed (retarded) according to the
vehicle speed.
[0005] Even if a relatively large vibration is generated on the vehicle body while the vehicle
front road wheel(s) have passed the road surface convex and recess, the preview control
such as to refer to the vibration input on the vehicle body at the time of the passages
of the front road wheels on the road surface convex and recess is carried out when
the rear road wheels pass on the same road surface convex and recess. Consequently,
when the rear road wheel passes on the same road surface convex and recess, the vibration
input on the vehicle body can be reduced as compared with the vibration input on the
vehicle body during the passage of the front road wheels on the road surface convex
and recess.
[0006] In the previously proposed suspension system, sensors used to detect the vibration
input are individually and independently installed at the respective road wheel attached
positions of the front and rear road wheels.
[0007] However, since sensors used to determine sprung mass vertical velocities and relative
velocities between the sprung mass and unsprung mass are required to be individually
and independently installed at the respective road wheel positions of the front and
rear road wheels, its system configuration becomes complex, it is difficult for such
sensors as described above to be mounted in the vehicle, and its system structure
manufacturing cost becomes accordingly high.
[0008] In addition, since sprung mass weights and suspension spring constants are different
in the case of the front road wheel side and of the rear road wheel side and sprung
mass resonance frequencies are different from each other of those on the front and
rear road wheel sides, it is not possible to make accurate estimations of the rear
road wheel positioned vehicular behavior only by previewing the vibration input from
the front road wheel side to the control of the damping force characteristics in the
rear road wheel positioned shock absorbers. Consequently, it is difficult to generate
an optimum control force for the rear road wheel positioned shock absorbers.
SUMMARY OF THE INVENTION:
[0009] It is an object of the present invention to provide apparatus and method for a vehicular
suspension system, the suspension system having a plurality of shock absorbers, each
of the shock absorbers being interposed between a sprung mass of a vehicle body and
an unsprung mass of a corresponding one of front and rear left and right road wheels,
which can achieve a simpler and less expensive construction of the apparatus with
sensors used to determine vehicular behavior at a left road wheel position omitted,
and which can accurately estimate the vehicular behavior at the rear road wheel position
so that an optimum control force is exhibited in each of the shock absorbers located
at the rear road wheel positions without execution of a, so-called, preview control.
[0010] According to one aspect of the present invention, there is provided with an apparatus
for a vehicular suspension system , said suspension system having a plurality of front
and rear left and right road wheel positioned shock absorbers, each shock absorber
being interposed between a sprung mass of a vehicle body and an unsprung mass of a
corresponding one of front left and right road wheels and rear left and right road
wheels, said apparatus comprising: a) damping force characteristic varying means for
operatively varying a damping force characteristic of each corresponding one of the
respective shock absorbers; b) front road wheel position vehicular behavior determining
means for determining a vehicular behavior at a front road wheel position of the vehicle
body and outputting a first signal indicative of the vehicular behavior at the front
road wheel position; c) rear road wheel position vehicular behavior estimating means
for estimating the vehicular behavior at a rear road wheel position of the vehicle
body from said first signal using a predetermined transfer function between a front
road wheel position and a rear road wheel position and outputting a second signal
indicative of the vehicular behavior at the rear road wheel position of the vehicle
body; d) control signal forming means for forming and outputting front road wheel
position control signals for the front left and right road wheel positioned shock
absorbers on the basis of said first signal and for forming and outputting rear road
wheel position control signals for the rear left and right road wheel positioned shock
absorbers on the basis of the second signal; and e) damping force characteristic controlling
means for controlling the damping force characteristics of the front left and right
road wheel positioned shock absorbers on the basis of the front road wheel position
control signals via said damping force characteristic varying means and for controlling
the damping force characteristics of the rear left and right road wheel positioned
shock absorbers on the basis of the rear road wheel position control signals via said
damping force characteristic varying means, respectively.
[0011] According to another aspect of the present invention, there is provided with an apparatus
for controlling a damping force characteristic for each of a plurality of vehicular
front and rear left and right road wheel positioned shock absorbers constituting a
vehicular suspension system, each of said shock absorbers being interposed between
a sprung mass of a vehicle body and an unsprung mass of a corresponding one of front
left and right road wheels and rear left and right road wheels, said apparatus comprising:
a) detecting means for detecting sprung mass vertical accelerations at front left
and right road wheel postions; b) first converting means for converting the detected
front left and right road wheel position sprung mass vertical accelerations into corresponding
sprung mass vertical velocities at the front left and right road wheel positions,
respectively;
c) first estimating means for estimating relative velocities betwen the sprung
mass and the unsprung mass at the front left and right road wheel positions from the
detected sprung mass vertical accelerations by said detecting means at the front left
and right road wheel positions, respectively, using a first predetermined transfer
function; d) second estimating means for estimating sprung mass vertical accelerations
at rear left and right road wheel positions from the detected sprung mass vertical
accelerations at the front left and right road wheel positions, respectively, using
a second predetermined transfer function; e) second converting means for converting
the sprung mass vertical accelerations at the rear left and right road wheel positions
estimated by said second estimating means into the sprung mass vertical velocities
at the rear left and right road wheel positions, respectively; f) third estimating
means for estimating relative velocities between the sprung mass and the unsprung
mass at the rear left and right road wheel positions from the detected sprung mass
vertical accelerations at the front left and right road wheel positions, respectively,
using a third predetermined transfer function; g) control signal forming means for
forming front left and right road wheel position control signals for the front left
and right road wheel positioned shock absorbers on the basis of the sprung mass vertical
velocities at the front left and right road wheel positions converted by said first
converting means and the relative velocities at the front left and right road wheel
positions estimated by said first estimating means and for forming rear left and right
road wheel position control signals for the rear left and right road wheel positioned
shock absorbers on the basis of the sprung mass vertical velocities at the rear left
and right road wheel positions converted by said second converting means and the relative
velocities at the rear left and right road wheel positions estimated by said third
estimating means; and h) damping force characteristic controlling means for controlling
the damping force characteristics of the front left and right road wheel positioned
shock absorbers on the basis of the front left and right road wheel position control
signals formed by said control signal farming means, respectively, and for controlling
the damping force characteristics of the rear left and right road wheel positioned
shock absorbers on the basis of the rear left and right road wheel position control
signals formed by said control signal forming means, respectively.
[0012] According to still another aspect of the present invention, there is provided with
a method for controlling a damping force characteristic for each of a plurality of
vehicular front and rear left and right road wheel positioned shock absorbers constituting
a vehicular suspension system, each of said shock absorbers being interposed between
a sprung mass of a vehicle body and an unsprung mass of a corresponding one of front
left and right road wheels and rear left and right road wheels, said method comprising
the steps of: a) detecting sprung mass vertical accelerations at front left and right
road wheel positions using front road wheel position sprung mass vertical acceleration
detecting means; b) converting the detected front left and right road wheel position
sprung mass vertical accelerations into corresponding sprung mass vertical velocities
at the front left and right road wheel positions, respectively; c) estimating relative
velocities between the sprung mass and the unsprung mass at the front left and right
road wheel positions from the detected sprung mass vertical accelerations at the step
a) at the front left and right road wheel positions, respectively, using a first predetermined
transfer function; d) estimating sprung mass vertical accelerations at rear left and
right road wheel positions from the detected sprung mass vertical accelerations at
the front left and right road wheel positions, respectively, using a second predetermined
transfer function; e) converting the sprung mass vertical accelerations at the rear
left and right road wheel positions estimated at the step d) into the sprung mass
vertical velocities at the rear left and right road wheel positions; f) estimating
relative velocities between the sprung mass and the unsprung mass at the rear left
and right road wheel positions from the detected sprung mass vertical accelerations
at the front left and right road wheel positions, respectively, using a third predetermined
transfer function; g) forming front left and right road wheel position control signals
(V
FL, V
FR) for the front left and right road wheel positioned shock absorbers on the basis
of the sprung mass vertical velocities at the front left and right road wheel positions
converted at the step b) and the relative velocities at the front left and right road
wheel positions estimated at the step c) and forming rear left and right road wheel
position control signals (V
RL, V
RR) for the rear left and right road wheel positioned shock absorbers on the basis of
the sprung mass vertical velocities at the rear left and right road wheel positions
converted at the step e) and the relative velocities at the rear left and right road
wheel positions estimated at the step f); and h) controlling the damping force characteristics
of the front left and right road wheel positioned shock absorbers SA
FL and SA
FR on the basis of the front left and right road wheel position control signals (V
FL, V
FR) formed at the step g) and controlling the damping force characteristics of the rear
left and right road wheel positioned shock absorbers SA
RL and SA
RR on the basis of the rear left and right road wheel position control signals (V
RL, V
RR) formed at the step g).
BRIEF DESCRIPTION OF THE DRAWINGS:
[0013]
Fig. 1 is an explanatory view of an arrangement of a vehicular suspension system damping
force controlling apparatus in a first preferred embodiment according to the present
invention.
Fig. 2 is a circuit block diagram of a control unit and its peripheral circuits of
the vehicular suspension system damping force controlling apparatus shown in Fig.
1.
Fig. 3 is a partially sectional view of each shock absorber SA used in the first embodiment
shown in Figs. 1 and 2.
Fig. 4 is an enlarged, partially sectional view of the representative shock absorber
SA shown in Fig. 3.
Fig. 5 is a characteristic graph representing damping forces with respect to a piston
speed of the representative shock absorber SA shown in Figs. 3 and 4.
Fig. 6 is a damping coefficient characteristic graph representing damping force control
regions corresponding to stepped positions of an adjuster installed in the representative
shock absorber SA, the adjuster being associated with a stepping motor and being pivoted
according to the rotation of the representative pulse (stepping) motor shown in Figs.
2 and 3.
Figs. 7A, 7B, and 7C are cross sectional views cut away along a line K - K of Fig.
4 representing an essential part of the representative shock absorber shown in Fig.
4.
Figs. 8A, 8B, and 8C are cross sectional views cut away along lines L - L and M -
M of Fig. 4 representing an essential part of the representative shock absorber SA
shown in Figs. 3 and 4.
Figs. 9A, 9B, and 9C are cross sectional views cut away along a line N - N of Fig.
4 representing an essential part of the representative shock absorber shown in Figs.
3 and 4.
Fig. 10 is a damping force characteristic graph when an extension stroke side (phase)
is in a hard (damping force) characteristic with respect to the piston of the representative
shock absorber SA shown in Fig. 4 (HS control mode).
Fig. 11 is a damping force characteristic graph when both extension and compression
stroke sides (phases) are in soft damping force states (SS control mode).
Fig. 12 is a damping force characteristic graph when the compression stroke side (phase)
is in a hard damping force state (SH control mode).
Fig. 13 is a circuit block diagram of a signal processing circuit in the suspension
system damping force characteristic controlling apparatus in the first embodiment
according to the present invention shown in Fig. 1 used to finally form a control
signal V (VFR, VFL, VRR, and VRL) and used to finally form a target damping force characteristic position P (PFR, PFL, PRR, and PRL) for each of front right and left road wheel positioned and of rear right and left
road wheel positioned shock absorber and for each of the front right and left and
rear right and left positioned stepping motors, respectively.
Fig. 14 is an operational flowchart executed in a control unit in the case of the
first embodiment according to the present invention.
Figs. 15A, 15B, 15C, 15D, and 15E are integrally a timing chart indicating a damping
force characteristic control operation of the control unit in the first preferred
embodiment according to the present invention.
Figs. 16A and 16B are characteristic graphs of gain and phase characteristics of velocity
converting filters in a semi-logarithmic scale (dotted lines denote a first-order
low pass filter and solid lines denote a phase advance (lead) compensation filter
(PCF) used in the first embodiment shown in Fig. 13.
Figs. 17A and 17B are characteristic graphs of gain and phase characteristics of combinations
of the velocity converting filter and an unnecessary component cutting band pass filter
(dotted lines denote a combination of a first-order low pass filter LPF and a first-order
band pass filter and solid lines denote another combination of the phase advance (lead)
compensation filter PCF and a second-order band pass filter) in the semi-logarithmic
scale, used in the first embodiment and its alternative, respectively.
Fig. 18 is an explanatory view for explaining a transfer function calculation model
adopted in the first embodiment shown in Figs. 1 and 2.
Figs. 19A and 19B are characteristic graphs of gain and phase characteristics of a
transfer function G5(S) from a sprung mass vertical acceleration at the front road wheel positions up to
a corresponding relative velocity between the sprung mass and unsprung mass in the
semi-logarithmic scale, in the case of the first embodiment.
Figs. 20A and 20B are characteristic graphs of gain and phase characteristics of a
transfer function GR(S) from front (left and right) road wheel position sprung mass vertical accelerations
up to rear (left and right) road wheel sprung mass vertical velocities in the semi-logarithmic
scale, in the case of the first embodiment.
Fig. 21A and 21B are characteristic graphs of gain and phase characteristics of a
transfer function GU(S) from the front (left and right) road wheel position sprung mass vertical accelerations
to the rear (left and right) road wheel position relative velocities between the sprung
mass and unsprung mass in the semi-logarithmic scale in the first embodiment.
Figs. 22A, 22B, 22C, 22D, 22E, and 22F are integrally a timing chart indicating actual
vehicle running test results as simulations.
Fig. 23 is a circuit block diagram of another signal processing circuit in the case
of a second preferred embodiment of the suspension system damping force characteristic
controlling apparatus according to the present invention.
Fig. 24 is a circuit block diagram of a still another signal processing circuit in
the case of a third preferred embodiment of the suspension system damping force characteristic
controlling apparatus according to the present invention.
Fig. 25 is an explanatory view (perspective view) for explaining another transfer
function calculation model in the third preferred embodiment of the suspension damping
force controlling apparatus.
Fig. 26 is an inversely proportional map indicating an alternative of an inversely
proportional function use in the case of the first embodiment.
Fig. 27A, 27B, 27C, 27D, and 27E are integrally a timing chart indicating the damping
force characteristic control operation of the control unit in a fourth embodiment
according to the present invention.
Fig. 28 is an operational flowchart for explaining a switching operation between a
basic damping force characteristic control by means of a basic control portion and
a correction damping force characteristic control by means of a correction control
portion executed in the control unit in the case of the fourth embodiment.
Fig. 29 is a signal timing chart for explaining the switching operation executed in
the control unit in the fourth embodiment shown in Fig. 28.
BEST MODE CARRYING OUT THE INVENTION:
[0014] Reference will hereinafter be made to the drawings in order to facilitate a better
understanding of the present invention.
(First Embodiment)
[0015] Fig. 1 shows a whole system configuration of a vehicular suspension system damping
force characteristic controlling apparatus in a first preferred embodiment according
to the present invention.
[0016] Four shock absorbers SA
FL, SA
FR, SA
RL, and SA
RR (it is noted that subscripts FL denotes a front left road wheel side (position),
FR denotes a front right road wheel side (position), RL denotes a rear left road wheel
side (position), RR denotes a rear right road wheel side (position), and a representative
shock absorber is simply denoted by SA since all shock absorbers (having the mutually
same structures) are interposed between given parts of a vehicular body (sprung mass)
and respective road (tire) wheels (unsprung mass). The road wheels comprise front
left road wheel, front right road wheel, rear left road wheel, and rear right road
wheel of the vehicle. It is noted that the above-described given parts of the vehicular
body indicate front left and right road wheel positions and rear left and right road
wheel positions.
[0017] As shown in Fig. 1, two vertical (.i.e., upward and downward) sprung mass acceleration
(G, G; gravity) sensors 1
FL and 1
FR are attached onto given parts (also called, tower positions) of the vehicular body
adjacent to the front left and right road wheel side shock absorbers SA (namely, SA
FL and SA
FR), each being provided to detect a vertical sprung mass acceleration acted upon the
sprung mass (vehicle body). A vehicle speed sensor 2 is provided which detects a vehicle
speed of the vehicle.
[0018] A control unit 4 is installed at a given part of the vehicle to receive signals derived
from the two acceleration sensors 1
FR and 1
FL and from the vehicle speed sensor 2, processes these signals, and outputs finally
drive signals to respective actuators (,i.e., stepping motors 3) for the respective
four shock absorbers SA (SA
FR, SA
FL, SA
RL, and SA
RR).
[0019] Fig. 2 shows a circuit block diagram of the vehicular shock absorber damping force
controlling apparatus in the first embodiment according to the present invention shown
in Fig. 1.
[0020] Referring to Figs. 1 and 2, the control unit 4 is installed on a portion of the vehicular
body near to a driver's seat. The control unit 4 includes: an input interface circuit
4a; a CPU (Central Processing Unit) 4b; a memory 4bb having a ROM (Read Only Memory)
and a RAM (Random Access Memory); an output interface 4aa, and actuator driver circuits
4c; and a common bus.
[0021] It is noted that, in the first embodiment, no stroke sensor used to determine a relative
velocity between the sprung mass and the unsprung mass at any of the front and rear
road wheel positions is used. The control unit 4 is provided with the respective drivers
4c connected between the output interface 4aa and the corresponding stepping motors
3.
[0022] The control unit 4 shown in Fig. 2 is provided with a signal processing circuit in
terms of its hardware structure as shown in Fig. 13. The signal processing circuit
derives each control signal V (including each target damping force characteristic
position P) used to perform a damping force characteristic control for each shock
absorber SA. The explanation of Fig. 13 will be described later.
[0023] Next, Fig. 3 show a cross sectional view of each shock absorber SA shown in Figs.
1 and 2.
[0024] The shock absorber SA, as shown in Fig. 3, includes: a cylinder 30, a (movable) piston
31 defining an upper portion chamber A and a lower portion chamber B; an outer envelope
33 in which a reservoir chamber 32 is formed on an outer peripheral end of the cylinder
30; a base 34 which defines the lower portion chamber B and the reservoir chamber
32; a guide member 35 which guides a sliding motion of a piston rod 7 with the other
end of which the movable piston 31 is linked; a suspension spring 36 interposed between
the outer envelope 33 and vehicle body; and a bumper rubber 37.
[0025] Each stepping motor 3 shown in Figs. 1 and 2 is installed in an upper position of
the corresponding one of the shock absorbers SA, as shown in Fig. 3, so as to operatively
rotate an adjuster 40 (refer to Fig. 4) via a control rod 70 in response to a rotation
drive signal from the corresponding one of the actuator drivers (circuits) 4c. A rotating
shaft of the corresponding one of the stepping motors 3 is mechanically connected
to the corresponding adjuster 40 within each shock absorbers SA via the control rod
70.
[0026] Fig. 4 shows an enlarged cross sectional view representing a part of the piston assembly
31 and its surrounding part of each of the shock absorbers SA.
[0027] As shown in Fig. 4, the piston 31 is formed with penetrating holes 31a and 31b therethrough.
In addition, the piston 31 is provided with a compression phase attenuation valve
20 and an extension phase attenuating valve 12, both of the valves 20, 12 respectively
opening and closing the respective penetrating holes 31a and 31b. A stud 38 is spirally
meshed with and fixed to a bound stopper 41 spirally meshed with and fixed to a tip
end of the piston rod 7.
[0028] The stud 38 is penetrated through the piston 31. In addition, the stud 38 is formed
with a communication hole 39 so as to communicate the upper portion chamber A and
the lower portion chamber B, the communication hole 39 forming flow passages (an extension
phase second flow passage E, extension phase third flow passage F, bypass flow passage
G, and compression phase second flow passage J as will be described later). Then,
the adjuster 40 which changes flow passage cross sectional areas of the above-described
flow passages is provided within the communication hole 39.
[0029] Furthermore, an extension stroke side (phase) check valve 17 and a compression (or
contraction) stroke side (compression phase) check valve 22 are also installed on
an outer periphery of the stud 38, which enable and disable the fluid flow through
the above-described flow passages formed by the communication hole 39 in accordance
with a direction of the flow of the fluid. As shown in Fig. 3, the adjuster 40 is
rotatable by means of the corresponding one of the actuators (stepping motors) 3 via
the control rod 70.
[0030] It is noted that the stud 38 is formed with a first port 21, a second port 13, a
third port 18, a fourth port 14, and fifth port 16, respectively, in an upper order.
[0031] On the other hand, referring to Fig. 4, the adjuster 40 is formed with a hollow portion
19, a first lateral hole 24, and a second lateral hole 25, both lateral holes communicating
the internal and external portions of the adjuster 40. A longitudinal groove 23 is
formed on an outer peripheral portion. Hence, four flow passages are formed between
the upper portion chamber A and lower portion chamber B as the fluid flow passages
when the piston stroke indicates the extension phase: that is to say, 1) an extension
stroke side (phase) first flow passage D such that the fluid passes the penetrating
hole 31b, a valve opened internal side of the extension stroke side (phase) attenuation
valve 12, and reaches the lower portion chamber B; 2) an extension stroke side (phase)
second flow passage E in which the fluid flows through the second port 13, the longitudinal
groove 23, the fourth port 14, a valve opened outer peripheral side of the extension
stroke side (phase) attenuation valve 12, and reaches the lower portion chamber B;
3) an extension stroke side (phase) third flow passage F in which the fluid passes
through the second port 13, the longitudinal groove 23, and the fifth port 16; and
4) a bypass flow passage G in which the fluid passes through the third port 18, the
second lateral hole 25, and the hollow portion 19 and reaches the lower portion chamber
B.
[0032] In addition, the three fluid flow passages through which the fluid can be caused
to flow during the compression stroke side (phase) of the piston 31 include: 1) a
compression stroke side (phase) first flow passage H in which the fluid flows through
the penetrating hole 31a and valve opened compression stroke side (phase) attenuation
valve 20; 2) a compression stroke side (phase) second flow passage J in which the
hollow portion 19, the first lateral hole 24, the first port 21, and the opened compression
stroke side (phase) check valve 22 and reaches the upper portion chamber A; and 3)
the bypass passage G in which the fluid flows through the hollow portion 19, the second
lateral hole 25, and the third port 18.
[0033] In summary, the shock absorber SA is so arranged and constructed as to be enabled
to change the damping force characteristics at a multiple stage in its damping characteristic,
as shown in Fig. 5, either in the extension phase or compression phase when the adjuster
40 is pivoted according to the rotation of the corresponding one of the stepping motors
3.
[0034] Fig. 6 shows relationships between the rotated position of the adjuster 40 and damping
force characteristics at both the extension stroke (phase) and compression phase with
respect to the piston 31.
[0035] In details, as shown in Fig. 6, when the adjuster 40 is pivoted in a given counterclockwise
direction from a generally center position at which both of the extension and compression
phases are in soft damping force characteristic positions (hereinafter, referred to
as a soft region (soft control mode) SS), the damping force coefficient at the extension
stroke side (phase) can be changed at the multiple stage from a maximum hard to a
minimum hard characteristic but the compression stroke side is fixed at a soft position
(hereinafter, referred to as an extension stroke side (phase) hard region HS). On
the contrary, when the adjuster 40 is pivoted in a given clockwise direction therefrom,
the damping force coefficient at the compression stroke side (phase) is only changeable
to a hard region from the maximum hard to the minimum hard characteristic at the multiple
stages and the damping force characteristic at in the compression stroke side is fixed
to the soft position (hereinafter, referred to as a compression hard region (compression
phase hard) SH).
[0036] When, as shown in Fig. 6, the adjuster 40 is pivoted at any one of positions ①, ②,
and ③, cross sections of the piston assembly portions cut away along lines K - K,
L - L, M - M, and N - N of Fig. 4 are respectively shown in Figs. 7A (①), 7B (②),
and 7C (③) (K-K), 8A (①), 8B (②), and 8C (③) (L - L, M - M), 9A (① ), 9B (②), and
9C (③) (N - N), respectively.
[0037] The damping force characteristics at the respective positions ①, ②, and ③ shown in
Fig. 6 are shown in Figs. 10, 11, and 12, respectively.
[0038] Fig. 10 shows the damping force characteristic of the representative shock absorber
SA when the adjuster 40 is positioned at ① of Fig. 6.
[0039] Fig. 11 shows that when the adjuster 40 is positioned at ② of Fig. 6.
[0040] Fig. 12 shows that when the adjuster 40 is positioned at ③ of Fig. 6.
[0041] Next, Fig. 14 shows an operational flowchart for explaining the content of the damping
force characteristic control operation for each shock absorber SA executed in the
control unit 4.
[0042] At a step 101, the CPU 4b determines whether the formed control signal V (for each
one of the shock absorbers SA) is increased and exceeds a predetermined positive threshold
value δ
T (it is noted that, in this embodiment,

) . If Yes at the step 101, the routine goes to a step 102 in which the corresponding
one of the shock absorber SA is set to as the extension phase hard region HS.
[0043] If NO at the step 101, the routine goes to a step 103 in which the CPU 4b determines
whether the control signal V is below a predetermined negative threshold value - δ
c (it is noted that, in this embodiment

).
[0044] If YES at the step 103, the routine goes to a step 104 in which the damping force
characteristic of the corresponding one of the shock absorbers SA is set to as the
compression phase hard region SH.
[0045] If NO at the step 103, the routine goes to a step 105, namely, if the CPU 4b determines
that the value of the control signal V gives zero, the corresponding one of the shock
absorbers SA is set to as each of the respective extension and compression phases
being in the soft region SS.
[0046] Fig. 15A through 15E show integrally a timing chart for explaining the operation
of the control unit 4 and shock absorber(s) SA in the case of the first embodiment.
[0047] When the control signal V formed on the basis of the sprung mass vertical velocity
Δx and relative velocity (Δx - Δx ₀) is varied with time as shown in Fig. 15A and
the control signal V indicates zero, the corresponding one of the shock absorbers
SA is controlled in the soft region SS. That is to say, each shock absorber SA, at
this time, is controlled in the SS mode in which both of the extension phase and compression
phase exhibit the predetermined fixed low damping force characteristics.
[0048] On the other hand, if the magnitude and direction of the control signal V indicates
positive, the corresponding one of the shock absorbers SA is controlled so that the
extension phase hard region HS is provided and the compression phase is fixed at a
predetermined low (soft) damping force characteristic. At this time, the damping force
characteristic at the extension phase is increased to provide a target damping force
characteristic position P
T in proportion to the magnitude of the control signal V .
[0049] If the direction of the control signal V, in turn, indicates negative, the compression
phase hard region SH is provided so that the extension phase damping force characteristic
is fixed to the low predetermined damping force characteristic and the damping force
characteristic at the compression phase is varied to provide a target damping force
characteristic position P
C in proportion to the value of the control signal V.
[0050] Next, a symbol a of Fig. 15C denotes a region in which the direction of the control
signal V formed on the basis of the sprung mass vertical velocity Δx and relative
velocity (Δx - Δx ₀) is inverted from the negative value (downward) to the positive
value (upward).
[0051] In the region a, the relative velocity (Δx - Δx ₀) still provides the negative value
(the phase of the shock absorber SA is at the compression phase) so that the corresponding
shock absorber SA is controlled at the extension phase hard region HS on the basis
of the direction of the control signal V and the phase of the corresponding shock
absorber SA is at the extension phase. Hence, at this region a, the extension phase
from which the piston 31 of the shock absorber SA is moved away provides the hard
characteristic which is proportional to the value of the control signal V.
[0052] A region b denotes a region in which the direction (direction discriminating sign)
of the control signal V is still positive (upward value) and the relative velocity
(Δx - Δx ₀) is switched from the negative value to the positive value (the phase with
respect to the piston of the corresponding shock absorber SA is the extension phase).
At this time, since the shock absorber SA is controlled in the mode of the extension
phase hard region HS on the basis of the direction of the control signal V, the stroke
direction of the corresponding shock absorber SA is the extension phase. Hence, at
the region b, the extension phase side of the shock absorber SA provides the hard
characteristic proportional to the value of the control signal V.
[0053] A region c denotes a region in which the control signal V is inverted from the positive
value (upward) to the negative value (downward) and the relative velocity (Δx - Δx
₀) still indicates positive (the phase of the corresponding one of the shock absorbers
SA is extension phase). However, at this region c, since the corresponding shock absorber
SA is controlled to the compression phase hard region SH on the basis of the direction
(direction discriminating sign) of the control signal V, this region c provides the
phase (in this region c, the extension phase is provided with the soft (predetermined
low damping force) characteristic.
[0054] A region d denotes a region in which the control signal V is still at the negative
value (downward) and the relative velocity (Δx - Δx ₀) is changed from the positive
value to the negative value (the phase at which the piston of the corresponding shock
absorber SA is at the extension phase side). At this time, since the corresponding
shock absorber SA is controlled at the compression phase hard region SH on the basis
of the direction of the control signal. Hence, the stroke (phase) of the corresponding
shock absorber SA is at the compression phase. In this region d, the compression phase
provides the hard characteristic proportional to the value of the control signal V.
[0055] As described above with reference to Figs. 15A through 15E, when the control signal
V based on the sprung mass vertical velocity Δx and relative velocity ( Δx - Δx ₀)
and the relative velocity of (Δx - Δx ₀) have the mutually the same direction discriminating
signs (regions b and d), the instantaneous phase at which the piston of the shock
absorber SA is moved is controlled at the hard characteristic mode. If the mutual
signs thereof (V and (Δx - Δx ₀)) are different from each other (regions a and c),
the phase, at the time of these regions, at which the piston of the corresponding
shock absorber SA is moved, is controlled in the soft characteristic. In the first
embodiment, the damping force characteristic control based on the Sky Hook theorem
(control theory) is carried out.
[0056] In the first embodiment, at a point of time when the phase at which the piston of
the corresponding one of the shock absorbers SA is moved is ended, namely, when the
region is transferred from the region a to the region b and from the region c to the
region d (hard characteristic to the soft characteristic), the damping force characteristic
position P
T or P
C at the phase to which the control is switched has already been switched to the hard
characteristic side at the previous regions a and c. Consequently, the switching from
the soft characteristic to the hard characteristic has been carried out without delay
in time.
[0057] Next, Fig. 13 shows the configuration of the signal processing circuit for forming
the control signal V and for deriving the target damping force characteristic position
P based on the control signal.
[0058] At a block B1, velocity converting filters (including two first-order low pass filters
LPF (L.P.F.) (dotted lines of Figs. 16A and 16B) or two phase advance compensation
filters (PCF, or P.C.F.) in the low pass filter types (solid lines of Figs. 16A and
16B) are used to convert the sprung mass vertical accelerations G
FL and G
FR at the front left and right road wheel positioned parts of the vehicle body into
corresponding sprung mass vertical velocities at the front left and right road wheel
positioned vehicle body. The gain characteristic and phase characteristic of both
of each of the first-order low pass filters LPFs and both of each of the phase advance
compensation filters PCFs are shown in Figs. 16A and 16B. It is noted that if the
phase advance compensation filters PCFs are used in place of the first-order low pass
filters LPFs, the corresponding sprung mass vertical accelerations (G) detected by
the sprung mass G sensors 1
FL and 1
FR can be converted into the velocity phases in a relatively wide frequency range.
[0059] Each phase advance compensation filter (P.C.F.) which may be used in place of the
corresponding one of the two first-order low pass filters in the block B1 of Fig.
13 has the following filter equation:

; and in a Z transformation equation (using a bilinear transformation equation),

, wherein A = 10, B = 0.001, K = 307 (gain value), y
(n) denotes the output at a time of (n), and X
(n) denotes the input at the time of (n). On the other hand, the filter equation of each
first-order low pass filter used in the block B1 is expressed as

wherein

, f denoting a frequency.
[0060] Then, at a block B2, the control unit 4 carries out a band pass filtering using two
band pass filters (BPFs) in order to cut off the signal components other than a target
frequency band to be controlled from the passed sprung mass velocity signals from
the first-order low pass filters provided at the block B1. In details, the two band
pass filters BPFs at the block B2 extract the front left and right road wheel positioned
sprung mass vertical velocities Δx (Δx
FL, Δx
FR) at the front road wheel positioned vehicle body with a vehicular sprung mass resonance
frequency band as a center of target.
[0061] Figs. 17A and 17B show the gain characteristics (Fig. 17A) and the phase characteristics
(Fig. 17B) due to the difference in combinations of the filters at the block B1 and
block B2.
[0062] The solid lines of Figs. 17A and 17B denote the gain and phase characteristics when
each phase compensation filter PCF and each second-order band pass filter BPF sorely
connected to the corresponding one of the phase advance compensation filter PCF are
used as the velocity converting filter and the band pass filter BPF at the blocks
B1 and B2 (NEW).
[0063] The dotted lines of Figs. 17A and 17B denote the gain (Fig. 17A) and phase characteristics
(Fig. 17B) of the combination of each first-order low pass filter (LPF) and each first-order
band pass filter (BPF) ( connected in series to the corresponding one of the low pass
filters LPFs) which are used for the velocity converting filter at the block B1 and
for the band pass filter at the block B2 (OLD).
[0064] As appreciated from Figs. 17A and 17B, the combination of each of the phase advance
compensation filters P.C.F. and each of the second-order band pass filters can have
a smaller value of gradient in the phase at the target control frequency band, the
target control frequency band corresponding to the sprung mass resonance frequency
band as compared with the combination of each of the first-order low pass filters
and each of the first-order band pass filters. It is noted that each of the band pass
filters at the block B2 may comprise the combination (mutually series connected) of
a low pass filter and a high-pass filter.
[0065] Next, at a block B3, front road wheel positioned relative velocity signals (Δx -
Δx ₀) [(Δx - Δx ₀)
FL, (Δx - Δx ₀)
FR] at the front left and right road wheel positioned sprung mass and unsprung mass
are derived from the front left and right road wheel positioned vertical accelerations
G
FL and G
FR, respectively, using the following transfer function G
5(S) from the sprung mass vertical accelerations at the front left and right road wheel
positions detected by the above-described sprung mass vertical acceleration (G) sensors
1
FL and 1
FR. The transfer function G
5(S) from the sprung mass vertical accelerations at the front left and right road wheel
positions to the corresponding relative velocities at the front left and right road
wheel positions is expressed as follows:

[0066] It is noted that S in the equation (1) denotes a Laplace operator and is generally
expressed as a complex variable (

, this is well known).
[0067] Fig. 18 shows an explanatory view of a transfer function calculation model used in
the first embodiment.
[0068] In Fig. 18, x₁ denotes a front road wheel side (position) sprung mass input (input
variable), x₂ denotes a front road wheel side (position) sprung mass input (variable),
x₃ denotes a front road wheel side (position) road surface (vibration) input (variable),
x₄ denotes a rear road wheel side (position) sprung mass input (variable), m₁ denotes
a front road wheel side (position) sprung mass, m₂ denotes a front road wheel side
(position) unsprung mass, c₁ denotes an attenuation coefficient of a front road wheel
side (position) suspension system (constituted by the front left and right road wheel
positioned shock absorbers), c₂ denotes an attenuation coefficient of each one of
the front left and right road wheels, k₁ denotes a spring constant of the front road
wheel side suspension system, k₂ denotes a spring constant of each of the front road
wheels, x₅ denotes a rear road wheel side (position) unsprung mass (vibration) input
(variable), x
3' denotes a rear road wheel side (position) road surface (vibration) input (variable),
m₃ denotes a rear road wheel side (position) unsprung mass, c₃ denotes an attenuation
coefficient of each of the rear left and right road wheels, c₄ denotes an attenuation
coefficient of each of the rear road wheel positioned road wheels, k₃ denotes a spring
constant of the rear road wheel side suspension system constituted by the rear left
and right road wheel positioned shock absorbers, and k₄ denotes a spring constant
of each of the rear left and right road wheels
[0069] Figs. 19A and 19B show the gain characteristic and phase characteristic of the above-defined
transfer function G
5(S).
[0070] Referring back to Fig. 13, at a block B4, control signals V
FL and V
FR used to control the damping force characteristics for the front left and right road
wheel positioned shock absorbers SA
FL and SA
FR are derived using the following equation (2) on the basis of the respective front
road wheel positioned sprung mass vertical velocities (signals) Δx (Δx
FL, Δx
FR) derived at the block B2 and the respective relative velocities (Δx - Δx ₀) [(Δx
- Δx ₀)
FL, (Δx - Δx ₀)
FR)] between the sprung mass and unsprung mass at the front left and right road wheel
positions. At the same block B3, the control unit 4 calculates the target damping
force characteristic positions P (P
FL, P
FR) in proportion to the corresponding control signals V
FL and V
FR, respectively, using the following equation (3).

[0071] If V ≧V
H,

(refer to Fig. 15A).
[0072] V
H denotes a threshold value of the proportional control of the damping force characteristic
and P
MAX denotes a maximum damping force characteristic position.
[0073] Since the control signal V is diverged into infinite when the relative velocity (
Δx - Δx ₀) at the denominator of the control signal derived using the equation (2),
in order to prevent this divergence, a minute threshold value X
min is set and when an absolute value of the relative velocity is equal to or below the
minute threshold value X
min (namely, |Δx - Δx ₀| ≦ X
min), the corresponding target damping force characteristic P is set to the maximum damping
force characteristic position P
MAX.
[0074] On the other hand, at a block B5, a delay processing is carried out for the front
left and right road wheel position sprung mass acceleration signals G
FL and G
FR detected by the vertical sprung mass sensors 1
FL and 1
FR in order to be used as rear road wheel positioned processing signals. That is to
say, in the first embodiment, a processing of a delay transfer function

, e denotes an exponential and is also expressed as

from among the transfer functions with the road surface inputs as transfer routes
is carried out which sets a delay time R

. The delay time R is the result of subtraction of a system response delay time φ
from the delay transfer function which is derived from the vehicle speed S
V and a wheel base length W
B and which corresponds to a time delay from the time at which the front road wheel
side road surface input x₃ occurs to the time at which the rear road wheel side road
surface input x
3' occurs. In this way, if the delay time R is set which is the subtraction of the system
response delay time φ from the division of W
B/S
V, the control force for the rear road wheel positioned shock absorbers can be generated
with the system response delay canceled. The delay processing is carried out before
the branched stage of the sprung mass vertical acceleration signals G
FR and G
FL to the block B1 so that the capacity of memory areas in the memory 4bb used during
its programming, namely, the memory capacity of the RAM can be reduced.
[0075] At the subsequent step B6, the rear left and right road wheel side (positioned) sprung
mass vertical acceleration signals G
RL and G
RR and the corresponding positioned relative velocity signals (Δx - Δx ₀)
RL (Δx -Δx ₀) between the sprung mass and unsprung mass are estimated (calculated) on
the basis of the following transfer functions G
R(S) and G
U(S) from (he front left and right road wheel positioned sprung mass vertical acceleration
signals G
FL and G
FR which are passed through the delay processing at the block B5. For the transfer function
calculation model, refer to Fig. 18.

[0076] It is noted that, in the equations (4) and (5), in each of the last equation items

and

, a part corresponding to the delay transfer function is omitted.
[0077] It is also noted that G
1(S) denotes the transfer function from one of the front road wheel positions up to the
road surface, G
2(S) denotes a delay transfer function in a input timing difference between the vehicle
body at one of the front road wheel positions and that at one of the rear road wheel
positions, G
3(S) denotes the transfer function from the road surface up to one of the rear road wheel
positioned sprung mass, and G
4(S) denotes the transfer function from the road surface up to one of the rear road wheel
positioned relative velocities.
[0078] It is further noted that, in the equations (4) and (5),

[0079] Figs. 20A and 20B show the gain and phase characteristics of the above-described
transfer function G
R(S).
[0080] Figs. 21A and 22B show the gain and phase characteristics of the above-described
transfer function G
U(S).
[0081] Referring back to Fig. 13, in the same way as the block B1, the velocity converting
filters (LPFs) are used at a block B7 to convert the estimated rear left and right
road wheel positioned sprung mass acceleration signals G
RL and G
RR into the corresponding rear left and right road wheel positioned sprung mass vertical
velocity signals.
[0082] At the subsequent block B8, the band pass filtering operation is carried out for
the rear road wheel left and right road wheel positioned vertical velocity signals
in order to cut off the frequency components other than the target frequency band
to be controlled, in the same way as carried out at the block B2. That is to say,
at the block B8, these band pass filters BPFs used at the block B8 serves to extract
the rear left and right road wheel positioned sprung mass vertical velocity signals
Δx (Δx
RL, Δx
RR) in the vehicle body sprung mass resonance frequency band which is the target of
control.
[0083] At a block B9, in the same way as carried out at the block B4 described above, control
signals V
RL and V
RR for the rear left and right road wheel positioned shock absorbers SA
RL and SA
RR are formed on the basis of the rear left and right road wheel positioned sprung mass
vertical velocity signals Δx (Δx
RL, Δx
RR) derived at the block B8 and on the basis of the rear left and right road wheel positioned
relative velocity signals between the sprung mass and unsprung mass (Δx - Δx ₀) [(Δx
- Δ x₀)
RL, (Δx - Δx ₀)
RR] using the above-described equation (2) and the target damping force characteristic
positions P (P
RL, P
RR) for the respective stepping motors 3 for the rear left and right road wheel positioned
shock absorbers SA
RL and SA
RR are calculated using the equation (3) which are proportional to the control signals
V
RL and V
RR.
[0084] As described above, the suspension system damping force controlling apparatus in
the first embodiment has the following advantages:
(1) In the suspension damping force characteristic controlling apparatus requiring
the front left and right road wheel positioned sprung mass vertical velocity signals
Δx FL, Δx FR, correspondingly positioned relative velocity signals (Δx - Δx ₀)FL, (Δx - Δx ₀)FR, the rear left and right road wheel positioned sprung mass vertical velocity signals
Δx RL, Δx RR, and the correspondingly positioned relative velocity signals (Δx - Δx ₀)RL and (Δx - Δx ₀)RR, only front left and right road wheel positioned vertical G sensors 1FL and 1FR are installed on the vehicle body corresponding positions as the sensors in the apparatus.
Hence, the other required sensors can be omitted. The system configuration can be
simplified so that an easiness in mounting the apparatus in the vehicle can be improved.
A system cost of manufacturing the suspension system damping force controlling apparatus
can be reduced.
(2) As compared with the previously proposed suspension system damping force characteristic
controlling apparatus described in the BACKGROUND OF THE INVENTION in which the vibration
input of the front road wheel side is used as the correction signal to merely preview
the damping force characteristic control for the rear road wheel positioned shock
absorbers, the sprung mass vertical velocities of the sprung mass at the rear road
wheel positions can accurately be estimated according to the transfer function from
the front road wheel side sprung mass vertical velocities up to the rear road wheel
side sprung mass vertical velocities with the road surface input as the transfer route.
Thus, the optimum control force can be generated.
Figs. 22A, 22B, 22C, 22D, 22E, and 22F show integrally a timing chart indicating results
of simulations on actual vehicle running tests.
Fig. 22A shows the actually measured sprung mass vertical velocity signal at one of
the front left and right road wheel positions.
Fig. 22B shows the actually measured relative velocity signal between the sprung mass
and unsprung mass at one of the front left and right road wheel positions.
Fig. 22C shows the actually measured rear road wheel position sprung mass vertical
velocity signal at one of the rear left and right road wheels.
Fig. 22D shows the actually measured relative velocity signal between the sprung mass
and the unsprung mass at one of the rear left and right road wheel positions.
Fig. 22E shows the rear road wheel side (position) sprung mass vertical velocity signal
derived using the transfer function described in the first embodiment.
Fig. 22F shows the rear road wheel side (position) relative velocity signal between
the sprung mass and the unsprung mass at one of the rear left and right positions
according to the transfer function in the first embodiment.
As appreciated from Fig. 22E, the rear road wheel side sprung mass vertical velocity
signal derived using the transfer function in the first embodiment can achieve such
a waveform as not to be enabled to be obtained by merely delaying the front road wheel
side sprung mass vertical velocity signal (particularly, refer to a part of the waveform
shown in Fig. 22E which is denoted by arrow marks of


). As compared with Fig. 22A, the rear road wheel side (position) sprung mass vertical
velocity signal derived using the transfer function shown in Fig. 22E which has the
characteristics of the gain and phase which are generally approximate to those of
the actually measured front road wheel side sprung mass vertical velocity signal shown
in Fig. 22A can be achieved.
(3) Since such a processing of the sprung mass vertical acceleration signals (GFL and GFR) using the delay transfer function which sets the delay time R which is the subtraction
of the system response delay time φ from the delay transfer function corresponding
to the time delay derived from the vehicular wheel base length WB and the vehicle speed SV from the time at which the front road wheel side road surface input x₃ to the time
at which the rear road wheel side road surface input x3' occurs is carried out from among the transfer functions with the road surface input
as the transfer route, as shown in Fig. 13, the control force can be generated at
the rear road wheel side (position) with the system response delay time canceled.
Consequently, the (more) optimum control force can be generated.
[0085] Next, second and third preferred embodiments of the suspension system damping force
controlling apparatus according to the present invention will be described below.
Since, in the second and third embodiments, the content of the signal processing circuit
is different from that of the first embodiment in the control unit 4, the other structures
are generally the same as those in the case of the first embodiment. Therefore, only
the different point from the first embodiment will be explained.
(Second Embodiment)
[0086] In the suspension system damping force controlling apparatus in a second preferred
embodiment, the following signal processing circuit shown in Fig. 23 is incorporated.
[0087] First, at a block C1, the velocity converting filters are used to convert the front
left and right road wheel position sprung mass vertical acceleration signals G
FL and G
FR at the front left and right road wheel positions detected by the two front road wheel
positioned sprung mass vertical acceleration (G) sensors 1
FL and 1
FR into the corresponding sprung mass vertical velocity signals, respectively, in the
same manner as carried out at the block B1 shown in Fig. 13.
[0088] At the subsequent block C2, the band pass filters (BPFs) (representatively expressed
as BPF in Fig. 23) are used to cut off the frequency components other than the target
frequency band to perform the control of the damping force characteristics of the
rear left and right road wheel positioned shock absorbers SA
RL and SA
RR, in the same manner as carried out at the block B2 shown in Fig. 13, so that the
sprung mass vertical velocity signals Δx
FL and Δx
FR at the rear left and right road wheel positions are derived.
[0089] On the other hand, at a block C3, in the same manner as carried out at the block
B3 of Fig. 13, the relative velocity signals between the sprung mass and the unsprung
mass at the front left and right road wheel positions (Δx - Δx ₀)
FL and (Δx - Δx ₀)
FR are calculated (estimated) using the transfer function G
5(S) from the respectively corresponding sprung mass vertical accelerations at the front
left and right road wheel positions up to the relative velocities between the sprung
mass and the unsprung mass at the respectively corresponding front left and right
road wheel positions (these are transfer routes) from the signals described below:
that is to say, from the front left and right road wheel positioned vertical acceleration
signals G
FL and G
FR detected by the two front road wheel positioned vertical acceleration (G) sensors
1
FL and 1
FR.
[0090] At a block C4, the sprung mass vertical acceleration signals G
RL and G
RR at the rear left and right road wheel position sprung mass are calculated on the
basis of a vertical transfer function G
gr(S) with the road surface input as its transfer route shown in the following equation
(6) and on the basis of a sprung mass forward/rearward transfer function G
gb(S) with the vehicle body sprung mass as its transfer route shown in the following equation
(7) from the front left and right road wheel position sprung mass vertical acceleration
signals G
FL and G
FR.
[0091] It is noted that the vertical transfer function G
gr(S) with the road surface input as its transfer route includes the delay transfer function

which sets the delay time

as described in the first embodiment with reference to Fig. 13.

[0092] It is noted that, in the equations (6) and (7), G
gr1(S) denotes a transfer function from one of the front left and right road wheel position
sprung mass vertical accelerations up to the road surface input of one of the front
left and right road wheels;
G
gr2(S) denotes a transfer function from the road surface input of one of the rear left and
right road wheels up to the corresponding one of the rear road wheel position sprung
mass vertical accelerations;
x
4r denotes a state variable in the vertical direction at the rear road wheel side transmitted
from the corresponding rear road wheel road surface input; and
x
4b denotes a state variable in the vertical direction at the rear road wheel side transmitted
from the front road wheel side via a transfer route defined in the vehicular forward/rearward
(longitudinal) direction (,i.e., front left road wheel side → rear left road wheel
side, front right road wheel side → rear right road wheel side).
[0093] It is also noted that the rear road wheel side (position) sprung mass state variable
x₄ is derived according to the following equation (8).

[0094] Referring back to Fig. 23, at a block C5, in the same manner as carried out at the
block C1 described above, the velocity converting filters are used to convert the
calculated sprung mass vertical acceleration signals G
RL and G
RR at the rear left and right road wheel positions into the sprung mass vertical velocity
signals at the rear left and right road wheel positions, respectively. At a block
C6, in the same manner as carried out at the block C2, the band pass filters (BPF)
is used to extract the sprung mass vertical velocity signal Δx
RL and Δx
RR at the rear left and right road wheel positions with the sprung mass resonance frequency
band as the target, respectively.
[0095] At a block C7, the relative velocity signals between the sprung mass and the unsprung
mass at the rear left and right road wheel positions denoted by (Δx - Δ x₀)
RL and (Δx - Δx ₀)
RR are calculated from the calculated sprung mass vertical acceleration signals G
RL and G
RR at the rear left and right road wheel positions at the block C4 using a transfer
function G
rr(S) (G
rr(S) is approximately equal to G
U(S)) from each of the rear road wheel sprung mass vertical accelerations up to the relative
velocity at the corresponding one of the rear left and right road wheel positions.
[0096] That is to say, in the second embodiment, at the block C4, the sprung mass vertical
acceleration signals G
RL and G
RR at the rear left and right road wheel positions are respectively derived from the
sprung mass vertical acceleration signals G
FL and G
FR at the front left and right road wheel positions using the transfer function G
gb(S) in the direction of the sprung mass forward/rearward direction with the vehicle body
sprung mass as the transfer route thereof in addition to the transfer function G
gr(S) in the vertical direction with the road surface input as the transfer route thereof.
The above-described matter is the difference point from the first embodiment.
[0097] Since the transfer function G
gb(S) in the sprung mass forward/rearward direction with the vehicle body sprung mass as
the transfer route is added, the rear road wheel side vehicular behaviors can further
accurately be estimated, the more optimum control force at the rear road wheel side
can be generated.
[0098] It is noted that the delay transfer function

which sets the delay time R

which is the subtraction of the system response delay time φ from the delay function
corresponding to the time delay from the time at which the front road wheel side road
surface input occurs to the time at which the rear road wheel side road surface input
occurs, the delay function being derived from the vehicular wheel base length W
B and the vehicle speed S
V, is included in the transfer function G
gr(S) in the vertical direction as the road surface input as its transfer route.
(Third Embodiment)
[0099] In the suspension system damping force controlling apparatus in a third preferred
embodiment, the following signal processing circuit in the control unit 4 shown in
Fig. 24 is incorporated.
[0100] The structure of the signal processing circuit shown in Fig. 24 is generally the
same as that in the case of the second embodiment shown in Fig. 23.
[0101] However, the difference point in Fig. 24 from that shown in Fig. 23 will be described
below.
[0102] In each block C4' of Fig. 24, the sprung mass vertical acceleration signals G
RL and G
RR at the rear left and right road wheel positions are calculated using a sprung mass
diagonal direction transfer function G
d(S) with the sprung mass as its transfer route as shown in the following equation (9)
in addition to the vertical direction transfer function G
gr(S) with the road surface input as its transfer route and the sprung mass forward/rearward
direction transfer function G
gb(S) with the sprung mass as the transfer route thereof (used in the case of the second
embodiment).
[0103] Fig. 25 shows the transfer function calculation model in the case of the third embodiment.
[0104] Since, in the third embodiment, the sprung mass diagonal direction transfer function
G
d(S) in which the sprung mass is its transfer route is added, the more accurate estimation
of the rear road wheel side vehicle behaviors can be made. Consequently, the more
optimum control force at the rear road wheel side shock absorbers SA
RL and SA
RR can be generated.

[0105] In the equation (9), x
1L denotes the state variable of the front left road wheel position sprung mass;
x
1R denotes the state variable of the front right road wheel side sprung mass;
x
4L denotes the state variable of the rear left road wheel position sprung mass caused
by the front right road wheel input;
x
4R denotes the state variable of the rear right road wheel position sprung mass caused
by the front left road wheel input;
x
4d denotes the state variable of the vertical direction at the rear road wheel positions
transmitted from the front road wheel positions via the transfer route in the diagonal
direction with respect to the vehicle body (front right road wheel side → rear left
road wheel side and front left road wheel side → rear right road wheel side) and is
derived using the above-described transfer function G
d(S).
[0106] In addition, the state variable of the rear road wheel side sprung mass x₄ is derived
from the following equation (10).

(Alternatives of the first, second, and third embodiments)
[0107] Although, in the first, second, and third embodiments, the sprung mass vertical G
sensors are installed on the sprung mass at the front left and right road wheel positions,
the number of installations of the sprung mass vertical G sensors are arbitrary. The
present invention is applicable to the suspension system having a single vertical
G (sprung mass vertical acceleration) sensor installed at the front road wheel position,
for eXample, a generally center of the front left and right road wheel positions.
[0108] Although, in the first, second, and third embodiments, such shock absorbers as having
the damping force characteristic varying means (adjuster) whose damping force characteristics
are controlled such that when the damping force characteristic at either one of the
extension and compression phases is variably controlled, the damping force characteristic
at the other phase of either of the extension and compression phase is controlled
to provide the low damping force characteristic, the present invention is applicable
to a vehicular suspension system having such shock absorbers that the damping force
characteristics at both of the extension and compression phases are variably controlled.
[0109] Although, in the first, second, and third embodiments, such transfer functions as
described in the equations (1), (4), (5), and so forth are used to derive the front
road wheel side relative velocity signals, the rear road wheel side sprung mass vertical
velocity signals, the rear road wheel side relative velocity signals between the sprung
mass and the unsprung mass, and the rear road wheel side sprung mass vertical acceleration
signals from the front road wheel side vertical acceleration signals, these transfer
functions indicate higher order functions. In this case, the transfer function equations
become complex and the capacity of programming becomes large. Alternatively, approximation
functions or approximation filters such as lower order transfer functions, normally
used band pass filters (BPFs) or high pass filters (HPFs) may be used whose gain and
phase characteristics are not varied in the frequency band requiring the control of
the damping force characteristics of the respective shock absorbers.
[0110] In addition, although, in each of the first, second, and third embodiment, the equation
(2) is used to derive the control signal V, the control signal may be derived using
a correction value KU derived from an inverse of the relative velocity (Δx - Δx ₀)
as described in the equation (11) in order to prevent the control signal from being
diverged to the infinite.

[0111] Furthermore, in place of the equation (11), a inverse proportional map shown in Fig.
26 may be used.
[0112] In Fig. 26, KU
max denotes a maximum value of KU fixed when the corresponding relative velocity (Δx
- Δ x₀) is equal to or below a predetermined lower limit threshold value S
min. As shown in Fig. 26, when the corresponding relative velocity (Δx - Δx ₀) becomes
equal to or below a predetermined upper limit value S
max, the correction value KU is fixed at a certain value.
[0113] Finally, although, in each of the first, second, and third embodiments, the above-described
equation (3) is used to derive the target damping force characteristic position P
from the corresponding control signal V, a dead zone V
NC may be provided for the control signal V in order to prevent the target damping force
characteristic position P from being in a hunting phenomenon due to minute upward
and downward directional movements of the control signal in the vicinity to zero.
In this case, the target damping force characteristic position P is derived as follows:

[0114] It is noted that the gain g of the equation (2) used to derive the control signal
V may be varied according to the vehicle speed detected by the vehicle speed sensor
2.
(Fourth Embodiment)
[0115] In the suspension system controlling apparatus of a fourth preferred embodiment according
to the present invention, the signal processing circuit in the control unit 4 described
in the first embodiment shown in Fig. 13 is incorporated although the other structures
are generally the same as those in the first embodiment.
[0116] In addition, the damping force characteristic control flowchart shown in Fig. 14
is incorporated in the fourth embodiment.
[0117] However, in the steps of 101 and 103, each vertical velocity signal Δx is compared
with zero.
[0118] At the step 102, the extension phase is varied in the hard damping force characteristic
with the compression phase fixed to the soft damping force characteristic, i.e., in
the HS control mode. At this time, the damping force characteristic at the extension
phase (the target damping force characteristic position P
T) is varied in proportion to the corresponding sprung mass vertical velocity Δx as
follows:

In the equation (13), α denotes a constant at the extension phase, K denotes a
gain variably set according to the corresponding sprung mass relative velocity (Δx
- Δx ₀).
[0119] At the step 104 in the fourth embodiment, the compression phase damping force characteristic
is controlled at the hard region with the extension phase characteristic fixed to
the soft damping force characteristic. The target damping force characteristic position
P
C, i.e., compression phase damping force characteristic is varied in proportion to
the corresponding sprung mass vertical velocity delta x as follows:

[0120] In the equation (14), β denotes a compression phase constant.
[0121] Next, Figs. 27A through 27E show integrally a timing chart indicating a switching
operation of control regions mainly in the representative shock absorber SA from among
the damping force characteristic control operations.
[0122] In Figs. 27A through 27E, the sprung mass vertical velocity Δx is taken as shown
in Fig. 27A and the the target damping force characteristic position P
T at the extension phase of each shock absorber SA (the drive signal for each corresponding
one of the stepping motors 3) P
T is at the plus side (positive) as shown in Fig. 27E and the target damping force
characteristic position at the compression phase of each shock absorber P
C (the drive signal for each corresponding one of the stepping motors 3) is at the
minus side (negative).
[0123] The other explanations of Figs. 27B, 27C, and 27D are generally the same as those
explained in the first embodiment with reference to Figs. 15B, 15C, and 15D, respectively.
Therefore the detailed explanations for Figs. 27B, 27C, and 27D are omitted here.
[0124] Next, a basic control on the damping force characteristics for the rear left and
right road wheel shock absorbers SA
RL and SA
RR and the content of a switching control operation to a corrective control from the
control operations in the control unit 4 will be described with reference to Fig.
28 and 29.
[0125] As shown in Fig. 28, at a step S201, the damping force characteristic position P
T at the extension phase in the basic control is derived on the basis of the following
equation (15).

[0126] In the equation (15) , Kr denotes a gain determined according to each of the rear
left and right road wheel position relative velocities between the sprung mass and
unsprung mass ((Δx - Δx ₀)
RL, (Δx - Δ x₀)
RR).
[0127] A the next step 202, the CPU 4b in the control unit 4 determines whether each of
the front road wheel side relative velocities V
Rf [(Δx - Δx ₀)
FL, (Δx - Δ x₀)
FR exceeds a predetermined threshold value V
RD.
[0128] If each of the front road wheel side relative velocities V
Rf exceeds the predetermined threshold value V
RD, the routine goes to a step 203 in which a correction control flag (Flag) is set
to 1. Thereafter, the routine goes to a step 204 in which a counting time of a timer
(Time) is reset to zero and, then, at a step 205, the timer is set to ON.
[0129] Thereafter, the routine goes to a step 206. If NO, namely, each of the front road
wheel side relative velocity V
Rf is not exceeded the predetermined threshold value V
RD, the routine jumps to the step 206.
[0130] At the step 206, the CPU 4b determines whether the correction control flag (Flag)
is set to 1. If YES at the step 206, the routine goes to a step 207. If NO at the
step 206, the routine goes to a step 211 in which the extension phase target damping
force characteristic position P is set to the damping force characteristic position
P
T at the extension phase at the basic control so that the associated stepping motor
3 is normally controlled.
[0131] On the other hand, at the step 207, the CPU 4b determines whether the time of the
timer (Time) is below a preset correction control ON time duration TH. If YES at the
step 207, namely, Timer < TH, the routine goes to a step 209 in which the correction
control flag Flag is reset to zero and the routine goes to the step 211 to return
to the normal basic damping force characteristic control (refer to a time TH₄ of Fig.
29).
[0132] At the step 208, the CPU 4b determines whether the damping force characteristic position
P
T at the extension phase during the basic damping force characteristic control operation
is below an extension phase limit position P
D set at a predetermined hard characteristic.
[0133] If YES at the step 208, the routine goes to a step 210 in which the extension phase
target damping force characteristic position P for the respective rear road wheel
side positioned shock absorbers SA
RL and SA
RR are set to the respective extension phase limit positions P
D so that the corresponding stepping motors 3 can speedily be driven so as to hole
the corresponding positions P
D (refer to TH₁ and TH₃ of Fig. 29). This is one routine. On the other hand, if P
T ≧ P₀ (NO at the step 208, the routine goes to the step 211 in which the target damping
force characteristic position P held at the position P
D is switched to the damping force characteristic position P
T and the associated stepping motor 3 is driven to approach to the target position
P
T.
[0134] The above-described routine shown in Fig. 28 is repeated for each predetermined time.
[0135] The content of switching control between the basic control and correction control
will be described with respect to the timing chart shown in Fig. 29.
(A) When the vehicle on which the suspension system damping force controlling apparatus
in the fourth embodiment has run on a normal road surface:
When the vehicle is running on a relatively good paved road having an abrupt convex
and recess, the front road wheel side relative velocity between the sprung mass and
the unsprung mass VRf [(Δx - Δx ₀)FL, (Δx - Δx ₀)FR] does not exceed the predetermined threshold value VRD. At this time, the extension phase damping force characteristic positions P at the
rear left and right road wheel positioned shock absorbers SARL and SARR are set to the target damping force characteristic positions PT at the basic control time which are proportional to the corresponding sprung mass
vertical velocities Δx RL and Δx RR in the same way as the compression phase. In this way, the optimum damping force
characteristic control based on the Sky Hook control theory is carried out.
(B) When the vehicle passes a road surface having a convex and recess (projection);
When the vehicle is running and immediately after one or each of the front left
and right road wheels has passed on a projection (convex and recess, unpaved road)
on the road surface, the vehicle body side of the sprung mass is inverted so as to
be decreased moderately but the unsprung mass of one of the vehicular road wheels
is turned to be abruptly decreased. Therefore, the front road wheel side relative
velocity VRf [(Δx - Δx ₀)FL and (Δx - Δx FR] exceeds the above-described predetermined threshold value VRD.
[0136] At this time, for a time during which the correction control ON time duration TH
has passed, the extension phase target damping force characteristic positions P are
set to the extension phase limit positions P
D which are the predetermined hard characteristic in the correction control mode.
[0137] That is to say, the switching control to the extension phase hard control region
HS is started. Thereafter, at a time point where the rear road wheels are about to
pass the projection by a predetermined delay, the switching to the extension phase
hard region HS is already completed or is about to a state where the switching thereto
is about to be completed. On the other hand, in the basic control, even if the rear
road wheel positioned shock absorbers are controlled from the front road wheel sprung
mass vertical velocities with the delay in the phase by the predetermined time, the
damping force characteristics at the rear left and right shock absorbers are controlled
in proportion to the sprung mass vertical velocities at a time point wherein the rear
road wheels pass the projection on the same road surface so that the damping force
characteristics at the extension phases are still in the soft characteristics.
[0138] However, in the correction control in the fourth embodiment, for the compression
phases due to the abrupt pushing ups of the unsprung mass to the sprung mass when
the rear road wheels pass the projection on the road surface, the compression phase
soft characteristics at the rear left and right shock absorbers SA
RL and SA
RR cause the transmission of the road surface input onto the vehicle body to be suppressed
without the time delay from a point of time at an initial stage of which the rear
road wheels pass the projection on the road surface.
[0139] Then, for the extension phases due to the abrupt drop of the unsprung mass immediately
after the vehicle rear road wheels have passes the projection on the road surface,
the extension hard characteristics of the rear left and right road wheel shock absorbers
SA
RL and SA
RR cause the abrupt drop of the unsprung mass to be suppressed without the time delay
at the time point wherein the rear road wheels have passed the projection. Consequently,
the unsprung mass huntings can be prevented due to the passage of the projection on
the road surface.
[0140] It is noted that the rear road wheel side damping force characteristic control based
on the relative velocity signals between the sprung mass and unsprung mass detected
and determined at the rear road wheel side cannot achieve the initially desired control
effect due to a delay in a control responsive characteristic for the abrupt vehicular
behavior when the rear road wheels pass such a projection on the road surface as described
above.
[0141] In addition, suppose that the damping force characteristic positions are expressed
in their numerical values so that the numerical values becomes larger as the damping
force characteristics at the extension phases give harder characteristics. When the
target damping force characteristic position P
T at the time of the basic control is below the extension phase limit position P
D. the correction control such that the extension hard characteristic is set to the
extension phase limit position P
D (the step 210 of Fig. 28). However, when the target damping force characteristic
position P
T exceeds the extension phase the extension phase limit position P
D, the target position P is set as the target damping force characteristic position
P
T (refer to the step 211 of Fig. 28).
[0142] It is noted that the above-described correction control ON time duration TH is variable
set on the basis of the following equation (16).

In the equation (16), W
B denotes the wheel base length (meter), Sv denotes the vehicle speed (Km/h), Δt (sec.)
denotes a constant time from a time at which the vibration input when the front road
wheel side relative velocities V
Rf at the front road wheel position exceed the predetermined threshold value V
RD is inputted to those at the rear road wheel position to a time at which the rear
road wheel side unsprung mass huntings are settled (Δt > 0).
[0143] The suspension system damping force characteristic controlling apparatus in the fourth
embodiment can achieve the following advantages:
(1) During the run on the normal (paved) road surface, the optimum damping force characteristic
control can be achieved on the basis of the Sky Hook control theory (theorem) by the
basic control operation. In addition, the transmission of the unsprung mass vibration
input to the sprung mass during the time at which the rear road wheels have passed
the projection on the road surface can be suppressed without delay in time according
to the compression phase soft characteristics by the correction control operation.
Furthermore, at a time immediately after the rear road wheels have passed the projection
of the road surface, the unsprung mass huntings can be prevented without delay in
time according to the extension phase hard characteristics.
Since the rear road wheel side shock absorber damping force characteristics can be
controlled on the basis of the relative velocities at the front road wheel side, the
vehicular driver's feeling of the unsprung mass huntings can be prevented without
a response delay.
(2) The switching from the soft damping force characteristic to the hard damping force
characteristic can be carried out without delay in time. Consequently, a high control
response characteristic can be achieved. The switching from the hard characteristic
to the soft characteristic can, in turn, be carried out without drive to the actuator
(each of the stepping motors 3). Thus, a durability of the actuator and power economy
can be achieved.
[0144] The other advantages in the case of the fourth embodiment are generally the same
as those in the case of the first embodiment.
1. An apparatus for a vehicular suspension system said suspension system having a plurality
of front and rear left and right road wheel positioned shock absorbers, each shock
absorber being interposed between a sprung mass of a vehicle body and an unsprung
mass of a corresponding one of front left and right road wheels and rear left and
right road wheels, said apparatus comprising:
a) damping force characteristic varying means for operatively varying a damping force
characteristic of each corresponding one of the respective shock absorbers;
b) front road wheel position vehicular behavior determining means for determining
a vehicular behavior at a front road wheel position of the vehicle body and outputting
a first signal indicative of the vehicular behavior at the front road wheel position;
c) rear road wheel position vehicular behavior estimating means for estimating the
vehicular behavior at a rear road wheel position of the vehicle body from said first
signal using a predetermined transfer function between a front road wheel position
and a rear road wheel position and outputting a second signal indicative of the vehicular
behavior at the rear road wheel position of the vehicle body;
d) control signal forming means for forming and outputting front road wheel position
control signals for the front left and right road wheel positioned shock absorbers
on the basis of said first signal and for forming and outputting rear road wheel position
control signals for the rear left and right road wheel positioned shock absorbers
on the basis of the second signal; and
e) damping force characteristic controlling means for controlling the damping force
characteristics of the front left and right road wheel positioned shock absorbers
on the basis of the front road wheel position control signals via said damping force
characteristic varying means and for controlling the damping force characteristics
of the rear left and right road wheel positioned shock absorbers on the basis of the
rear road wheel position control signals via said damping force characteristic varying
means, respectively.
2. An apparatus for a vehicular suspension system as claimed in claim 1, wherein said
predetermined transfer function used in said rear road wheel position vehicular behavior
estimating means comprises a vertical directional transfer function with a road surface
input as its transfer route.
3. An apparatus for a vehicular suspension system as claimed in claim 1, wherein said
predetermined transfer function used in said rear road wheel position vehicular behavior
estimating means comprises a first vertical directional vehicle body transfer function
with a road surface input as its transfer route and a second forward-rearward directional
vehicle body transfer function with the sprung mass of the vehicle body as its transfer
route.
4. An apparatus for a vehicular suspension system as claimed in claim 1, wherein said
front road wheel position determining means comprises two sprung mass acceleration
sensors, located separately from each other in a vehicular width direction at the
front road wheel position of the vehicle body.
5. An apparatus for a vehicular suspension system as claimed in claim 1, wherein said
front road wheel position vehicular behavior determining means comprises two sprung
mass acceleration sensors, located separately from each other in a vehicular width
direction at the front road wheel position of the vehicle body and wherein said predetermined
transfer function comprises a first vertical directional vehicle body transfer function
with a road surface input as its transfer route, a second forward-rearward directional
vehicle body transfer function with the sprung mass of the vehicle body as its transfer
route, and a third sprung mass diagonal line directional transfer function with the
sprung mass of the vehicle body as its transfer route.
6. An apparatus for a vehicular suspension system as claimed in claim 2, wherein said
front road wheel position vehicular behavior determining means comprises: front road
wheel position sprung mass vertical acceleration detecting means for detecting a front
road wheel position sprung mass vertical acceleration and outputting a detected front
road wheel position sprung mass acceleration signal indicative of the detected front
road wheel position sprung mass acceleration and front road wheel position sprung
mass vertical velocity determining means for converting the front road wheel position
vertical acceleration signal into a front road wheel position vertical velocity signal
indicating a front road wheel position sprung mass vertical velocity (Δx, Δx FL and Δx FR).
7. An apparatus for a vehicular suspension system as claimed in claim 6, wherein said
front road wheel position vehicular behavior determining means further comprises front
road wheel position relative velocity determining means for determining a front road
wheel position relative velocity between the sprung mass and the unsprung mass from
the detected front road wheel position sprung mass vertical acceleration signal using
the following predetermined transfer function:

wherein G
5(S) denotes the transfer function from the front road wheel position sprung mass vertical
acceleration to the front road wheel position relative velocity between the sprung
mass and the unsprung mass, m₁ denotes a front road wheel position sprung mass, S
denotes a Laplace operator, c₁ denotes an attenuation constant of either corresponding
one of the front road wheel positioned shock absorbers (SA
FL and SA
FR) constituting a front road wheel position suspension, k₁ denotes a spring constant
of the front road wheel position suspension.
8. An apparatus for a vehicular suspension system as claimed in claim 7, wherein said
rear road wheel position behavior estimating means comprises: rear road wheel position
sprung mass vertical acceleration estimating means for estimating a rear road wheel
position sprung mass vertical acceleration from the front road wheel position sprung
mass vertical acceleration signal using the following predetermined transfer function:

wherein G
1(S) denotes a transfer function from the front road wheel position sprung mass up to
a road surface on which the vehicle is to run, G
2(S) denotes a delay transfer function corresponding to an input time difference between
the front road wheel position vehicle body to the rear road wheel position vehicle
body, G
3(S) denotes a transfer function from the road surface to the rear road wheel position
sprung mass, x
4(S) denotes the transfer function on a rear road wheel position sprung mass input, and
x
1(S) denotes the transfer function on a rear road wheel position sprung mass input.
9. An apparatus for a vehicular suspension system as claimed in claim 8, wherein said
rear road wheel position vehicular behavior estimating means comprises rear road wheel
position relative velocity estimating means for estimating a rear road wheel position
relative velocity between the sprung mass and the unsprung mass from the front road
wheel position sprung mass acceleration signal using the following predetermined transfer
function as follows:

wherein G
4(S) denotes the transfer function from the road surface up to the rear road wheel position
relative velocity and x
5(S) denotes the transfer function on a rear road wheel position unsprung mass input.
10. An apparatus for a vehicular suspension system as claimed in claim 9, wherein said
front road wheel position control signals comprises a first control signal V
FL for the front left road wheel positioned shock absorber SA
FL and a second signal V
FR for the front right road wheel positioned shock absorber SA
FR and wherein said rear road wheel position control signals comprise a third control
signal V
RL for the rear left road wheel positioned shock absorber SA
RL and a fourth control signal V
RR for the rear right road wheel positioned shock absorber SA
RR, each control signal being formed on the basis of the following equation:

wherein (Δx - Δx ₀) denotes the relative velocity between the sprung mass and
the unsprung mass at a corresponding one of the front left and right and rear left
and right road wheel positions (Δx - Δx ₀)
FL, (Δx - Δx ₀)
FR, (Δx - Δx ₀)
RL, and (Δx - Δx ₀)
RR, and g denotes a control gain and wherein a target damping force characteristic position
P for said damping force characteristic varying means so that either extension phase
or compression phase to be controlled is varied so as to provide said target damping
force characteristic position P as follows:

, wherein P
max denotes a maximum damping force characteristic position, and V
H denotes a threshold value of a proportional range of each control signal.
11. An apparatus for a vehicular suspension system as claimed in claim 10, which further
comprises a vehicle speed sensor which is so arranged and constructed as to generate
and output a vehicle speed signal indicative of a vehicle speed and wherein said control
gain g in each of the control signals is varied according to a magnitude of the vehicle
speed.
12. An apparatus for a vehicular suspension system as claimed in claim 3, wherein said
front road wheel position vehicular behavior determining means comprises front road
wheel position sprung mass vertical acceleration detecting means for detecting a sprung
mass vertical acceleration at the front road wheel position and outputting a front,
road wheel position sprung mass vertical acceleration signal indicative thereof and
said rear road wheel position vehicular behavior estimating means comprises rear road
wheel position sprung mass vertical acceleration estimating means for estimating a
rear road wheel position sprung mass vertical acceleration from said front road wheel
position vertical sprung mass vertical acceleration signal using the following predetermined
transfer functions:

wherein S denotes a Laplace operator, G
gr(S) denotes the vertical directional transfer function with the road surface input as
its transfer route, X
4r(S) denotes the transfer function on a state variable in the vertical direction transmitted
from a rear road wheel position road surface input, x
1(S) denotes the transfer function on a front road wheel position sprung mass input, G
gr1(S) denotes the transfer function from the front road wheel position sprung mass vertical
acceleration up to a front road wheel position road input, G
D(S) denotes a delay transfer function, and G
gr2(S) denotes the transfer function from a rear road wheel position road surface input
up to the rear road wheel position sprung mass vertical acceleration, and

wherein G
gb(S) denotes the sprung mass forward/rearward directional transfer function with the vehicle
body sprung mass as its transfer route, X
4b(S) denotes the transfer function on a state variable in the vertical direction at the
rear road wheel position transmitted from the front road wheel position via a transfer
route set in the vehicle body forward/rearward direction (front left road wheel position
→ rear left road wheel position and front right road wheel position → rear right road
wheel position, and wherein

, wherein x₄ denotes a rear road wheel position sprung mass state variable.
13. An apparatus for a vehicular suspension system as claimed in claim 12, which further
comprises a vehicle speed sensor which is so arranged and constructed as to generate
and output a vehicle speed signal indicating a vehicle speed (Sv) and wherein G
D(S) is expressed as e-
SR, wherein e denotes an exponential (exp), R denotes a delay time and is expressed
as follows:

wherein W
B denotes a wheel base length of the vehicle and φ denotes a system response delay
time of the apparatus.
14. An apparatus for a vehicular suspension system as claimed in claim 13, wherein said
rear road wheel position sprung mass vertical acceleration estimating means estimates
the rear road wheel position sprung mass vertical acceleration using the predetermined
transfer functions as G
gr(S) and G
gb(S) and using the following predetermined transfer function:

wherein G
d(S) denotes the transfer function in a diagonal direction of the sprung mass with the
vehicle body sprung mass as its transfer route, x
4L(S) denotes the transfer function on a state variable of a rear left sprung mass, x
1R(S) denotes the transfer function on a state variable of a front right road wheel position
sprung mass, and x
4R(S) denotes the transfer function on a state variable of a rear right road wheel position,
and wherein a rear road wheel position sprung mass state variable x₄ is expressed
as

, wherein X
4d denotes a state variable in the vertical direction at the rear road wheel position
transmitted from the front road wheel position with the diagonal direction (front
left road wheel position → rear right road wheel position and front right road wheel
position → rear left road wheel position) and is derived from G
d(S).
15. An apparatus for a vehicular suspension system as claimed in claim 14, wherein each
control signal V is expressed as follows:

, wherein Δx denotes the sprung mass vertical velocity determined on the basis of
the sprung mass vertical acceleration signal at a corresponding one of the front left
and right road wheel positions and the rear left and right road wheel positions, ku
denotes a correction value derived from an inverse of a corresponding one (Δx - Δx
₀) of front left and right road wheel position and rear left and right road wheel
position relative velocities between the sprung mass and the unsprung mass determined
and estimated by said front road wheel position vehicular behavior determining means
and said rear road wheel vehicular behavior estimating means.
16. An apparatus for a vehicular suspension system as claimed in claim 10, wherein said
damping force characteristic controlling means comprises basic controlling means for
basically controlling the damping force characteristic of each one f the front left
and right road wheel position shock absorbers (SAFL, SAFR, SARL, SARR) so as to provide a hard characteristic when a direction discriminating sign of each
corresponding one of the sprung mass vertical velocities at the front left and right
road wheel positions is coincident with that of each corresponding one of the relative
velocities at the front left and right road wheel positions and at the rear left and
right road wheel positions and so as to provide a soft characteristic when the direction
discriminating sign of each corresponding one of the sprung mass vertical velocities
at the front left and right road wheel positions is not coincident with that of each
corresponding one of the relative velocities at the front left and right road wheel
positions and at the rear left and right road wheel positions.
17. An apparatus for a vehicular suspension system as claimed in claim 16, wherein when
the direction discriminating sign of each sprung mass vertical velocity is positive,
the direction of each sprung mass vertical velocity indicates upward with respect
to the vehicle body, when that of each sprung mass vertical velocity is negative,
the direction of each sprung mass vertical velocity indicates downward, when that
of each relative velocity between the sprung mass and the unsprung mass is positive,
each corresponding one of the front left and right road wheel and rear left and right
road wheel positioned shock absorbers indicates an extension phase, and when that
of each relative velocity between the sprung mass and unsprung mass is negative, each
corresponding one of the front left and right and rear left and right road wheel positioned
shock absorbers indicates a compression phase.
18. An apparatus for a vehicular suspension system as claimed in claim 17, wherein said
damping force characteristic controlling means further comprises correction controlling
means for fixing damping force characteristics of the rear left and right road wheel
positioned shock absorbers to respectively same predetermined ones of the hard characteristics
within a predetermined control time (TH) after the respectively corresponding road
wheel position extension phase relative velocities (VRf) at the front left and right road wheel positions estimated by the front road wheel
position relative velocity estimating means exceed a predetermined control threshold
value (VRD).
19. An apparatus for a vehicular suspension system as claimed in claim 18, which further
comprises a vehicle speed sensor which is so arranged and constructed as to generate
and output a vehicle speed signal indicative of a vehicle speed (Sv) and wherein said
predetermined control time (TH) is varied according to a magnitude of the vehicle
speed signal.
20. An apparatus for a vehicular suspension system as claimed in claim 19, wherein said
predetermined control time (TH) is set as follows:

wherein W
B denotes a wheel base length and Δt denotes a constant time duration from a time at
which an input when the front road wheel position relative velocity (V
Rf between the sprung mass and the unsprung mass exceeds the predetermined threshold
value (V
RD is inputted to the rear road wheel position to a time at which a hunting of the unsprung
mass at the rear road wheel position is settled (Δt > 0).
21. An apparatus for controlling a damping force characteristic for each of a plurality
of vehicular front and rear left and right road wheel positioned shock absorbers constituting
a vehicular suspension system, each of said shock absorbers being interposed between
a sprung mass of a vehicle body and an unsprung mass of a corresponding one of front
left and right road wheels and rear left and right road wheels, said apparatus comprising:
a) detecting means for detecting sprung mass vertical accelerations at front left
and right road wheel postions;
b) first converting means for converting the detected front left and right road wheel
position sprung mass vertical accelerations into corresponding sprung mass vertical
velocities at the front left and right road wheel positions, respectively;
c) first estimating means for estimating relative velocities betwen the sprung mass
and the unsprung mass at the front left and right road wheel positions from the detected
sprung mass vertical accelerations by said detecting means at the front left and right
road wheel positions, respectively, using a first predetermined transfer function;
d) second estimating means for estimating sprung mass vertical accelerations at rear
left and right road wheel positions from the detected sprung mass vertical acelerations
at the front left and right road wheel positions, respectively, using a second predetermined
transfer function;
e) second converting means for converting the sprung mass vertical accelerations at
the rear left and right road wheel positions estimated by said second estimating means
into the sprung mass vertical velocities at the rear left and right road wheel positions,
respectively;
f) third estimating means for estimating relative velocities between the sprung mass
and the unsprung mass at the rear left and right road wheel positions from the detected
sprung mass vertical accelerations at the front left and right road wheel positions,
respectively, using a third predetermined transfer function;
g) control signal forming means for forming front left and right road wheel position
control signals for the front left and right road wheel positioned shock absorbers
on the basis of the sprung mass vertical velocities at the front left and right road
wheel positions converted by said first converting means and the relative velocities
at the front left and right road wheel positions estimated by said first estimating
means and for forming rear left and right road wheel position control signals for
the rear left and right road wheel positioned shock absorbers on the basis of the
sprung mass vertical velocities at the rear left and right road wheel positions converted
by said second converting means and the relative velocities at the rear left and right
road wheel positions estimated by said third estimating means; and
h) damping force characteristic controlling means for controlling the damping force
characteristics of the front left and right road wheel positioned shock absorbers
on the basis of the front left and right road wheel position control signals formed
by said control signal forming means, respectively, and for controlling the damping
force characteristics of the rear left and right road wheel positioned shock absorbers
on the basis of the rear left and right road wheel position control signals formed
by said control signal forming means, respectively.
22. A method for controlling a damping force characteristic for each of a plurality of
vehicular front and rear left and right road wheel positioned shock absorbers constituting
a vehicular suspension system, each of said shock absorbers being interposed between
a sprung mass of a vehicle body and an unsprung mass of a corresponding one of front
left and right road wheels and rear left and right road wheels, said method comprising
the steps of:
a) detecting sprung mass vertical accelerations at front left and right road wheel
positions using front road wheel position sprung mass vertical acceleration detecting
means;
b) converting the detected front left and right road wheel position sprung mass vertical
accelerations into corresponding sprung mass vertical velocities at the front left
and right road wheel positions, respectively;
c) estimating relative velocities between the sprung mass and the unsprung mass at
the front left and right road wheel positions from the detected sprung mass vertical
accelerations at the step a) at the front left and right road wheel positions, respectively,
using a first predetermined transfer function;
d) estimating sprung mass vertical accelerations at rear left and right road wheel
positions from the detected sprung mass vertical accelerations at the front left and
right road wheel positions, respectively, using a second predetermined transfer function;
e) converting the sprung mass vertical accelerations at the rear left and right road
wheel positions estimated at the step d) into the sprung mass vertical velocities
at the rear left and right road wheel positions;
f) estimating relative velocities between the sprung mass and the unsprung mass at
the rear left and right road wheel positions, from the detected sprung mass vertical
accelerations at the front left and right road wheel positions, respectively, using
a third predetermined transfer function;
g) forming front left and right road wheel position control signals (VFL, VFR) for the front left and right road wheel positioned shock absorbers on the basis
of the sprung mass vertical velocities at the front left and right road wheel positions
converted at the step b) and the relative velocities at the front left and right road
wheel positions estimated at the step c) and forming rear left and right road wheel
position control signals (VRL, VRR) for the rear left and right road wheel positioned shock absorbers on the basis of
the sprung mass vertical velocities at the rear left and right road wheel positions
converted at the step e) and the relative velocities at the rear left and right road
wheel positions estimated at the step f); and
h) controlling the damping force characteristics of the front left and right road
wheel positioned shock absorbers SAFL and SAFR on the basis of the front left and right road wheel position control signals (VFL, VFR) formed at the step g) and controlling the damping force characteristics of the rear
left and right road wheel positioned shock absorbers SARL and SARR on the basis of the rear left and right road wheel position control signals (VRL, VRR) formed at the step g)